This invention relates to the preparation of polysilacyclosilazanes from 1,1-dichloro-1-silacyclobutane. These materials are useful as intermediates to form crosslinkable preceramic polymers which are useful to form ceramic materials upon pyrolysis.
What is disclosed herein is a novel process to obtain new and novel polymers which contain a strained ring silacycle in the polymer structure.
The process consists of forming polysilacyclobutasilazanes from dichloro substituted silacyclobutane and difunctional nucleophiles containing nitrogen atoms having at least one active proton on each nitrogen atom, in an inert, essentially anhydrous atmosphere at temperatures below room temperature. The intensive study of the chemistry of organosilicon heterocycles was precipitated in the late 1950's and increased substantially in the early 1960's. Many papers have been written on the formation of the organosilicon heterocycles and their ring opening capabilities. For example, Goodwin, in U.S. Pat. No. 2,607,791 issued on Aug. 19, 1952, describes the preparation of "cyclic silahydrocarbons" by reacting alkali metal with a mixture of R.sub.2 XSiCH.sub.2 SiXR.sub.2 and (XCH.sub.2).sub.2 SiR.sub.2, in the liquid phase wherein R is an alkyl group and X represents a halogen atom, to give fluid cyclic compounds of the type (CH.sub.2 SiR.sub.2).sub.n wherein in this example, n=3. Goodwin alludes to the existence of the possibility of preparing cyclics wherein n is equal to 3 to 50. J. Laave, in an article entitled, "Synthesis of Silacyclobutane and Some Related Compounds", JACS, 89:5, Mar. 1, 1967, pp. 1144-1147, shows the preparation of 1,1-dichloro-1-silacyclobutane by contacting magnesium powder in ethyl ether with 3-chloropropyltrichlorosilane. The polymerization of these heterocyclic silicon compounds was also studied extensively during the same time frame. Sommer, In U.S. Pat. No. 3,046,291, issued July. 24, 1962, discloses, for example, the process of preparing essentially linear carbon silicon polymers of the type (CH.sub.2 SiR.sub.2).sub.n wherein at least one R is hydrogen or chlorine, by thermally opening the silacyclobutane ring by heating to temperatures of 50.degree. C. to 200.degree. C. Sommer also notes that different types of polymers can be obtained if the polymerization takes place in the presence of oxygen and/or water, in that, oxygen is introduced randomly into the polymer to form siloxane linkages, resulting in random siloxane, silmethylene copolymers.
Nelson, in U.S. Pat. No. 3,398,178, issued Aug. 20, 1968, discloses the polymerization of silacyclobutanes to provide fluids, gums and elastomers. The polymerization involves a method of polymerizing with a catalytic amount of a compound selected from R".sub.m X.sub.n SiH.sub.4-m-n, AlX.sub.3 and HX to give a polymer consisting essentially of (SiR.sub.2 CH.sub.2 CHR'CH.sub.2) units. In the case where R".sub.m X.sub.n SiH.sub.4-m-n is used, chlorosilanes are indicated as being useful. Thus, 1,1-dimethyl-1-silacyclobutane was reacted with (CH.sub.3).sub.3 SiCl to give a polymer having the repeating unit (Si(CH.sub.3).sub.2 CH.sub.2 CH.sub.2 CH.sub.2). In U.S. Pat. No. 3,445,495, issued May 20, 1969, Nelson shows the polymerization of silacyclobutanes and disilacyclobutanes using a platinum-containing material as the catalyst. The polymers so-produced, contain units of the formula (SiR.sub.2 CH.sub.2 CHR'CH.sub.2) and/or (SiR.sub.2 CH.sub.2 SiR.sub.2 CH.sub.2). Later, in 1972, in U.S. Pat. No. 3,687,995, issued Aug. 29, 1972, Jonas et al. disclose the formation of novel silacyclobutanes which they alleged were useful as cross-linking agents and intermediates for organosilicon polymers. The novelty of the silacyclobutanes was the presence of functional groups on the silicon atom that were reactive with silanol functional organopolysiloxanes. Such functional groups on silicon were described as alkoxy and amino radicals. Jonas et al. also describes the novel materials as being useful as intermediates in the preparation of organosilicon resins and compounds containing silacyclobutane structures, but Jonas et al. do not describe even in a general sense, which organosilicon resins and compounds are useful, or how one skilled in the art may approach such preparations. However, in 1973, Jonas et al. disclosed organosilicon polymers containing silacyclobutane structures, in U.S. Pat. No. 3,719,696, issued Mar. 6, 1973. Such polymers, containing CH.sub.2 CHRCH.sub.2 (R'.sub.m) SiO.sub.2-m units derived by the hydrolysis or cohydrolysis of silanes of the formula CH.sub.2 CHRCH.sub.2 (R'.sub.m)SiY.sub.2-m lead to polymers containing strained ring silacycles in the organosilicon polymer itself. Both homopolymers and copolymers with R.sub.n SiO.sub.4-n or (SiR".sub.2 CH.sub.2 SiR".sub.2) are described, a special point being made by Jonas et al. at column 2lines 54 et seq., that polymers are formed containing terminal silacyclobutane structures which lead to crosslinkable rubbery products useful in the manufacture of organosilicon based elastomers.
Silazanes in general have been academic curiosities for many years and a variety of such silazanes, including monomers, oligomers, cyclics, low molecular weight and high molecular weight resins and linears have been prepared by a variety of methods.
For example, L. W. Breed et al., in the Journal of Organic Chemistry, 27, 1114 (1962) report the formation of silazanes from the polymerization of sterically hindered silazane oligomers, while in the Journal of Polymer Science, A 245 (1964), cyclic trimer and tetramer silazanes are reported to be thermally cracked, using catalysts to give linear polymers.
In contrast, fluids, rubber polymers and resins prepared from CH.sub.3 SiCl.sub.2 (CH.sub.2).sub.2 SiCl.sub.2 and excess ammonia have been reported by Kruger et al. in the Journal of Polymer Science, A 2 3179 (1964).
The patent literature also contains disclosures of the preparation of silazanes. Cheronis, in U.S. Pat. No. 2,564,674 discloses the preparation of low molecular weight linear silazane polymers by the reaction of halosilanes with excess ammonia in a solvent solution. Bausma, et al., in U.S. Pat. No. 3,809,713 discloses a similar reaction scheme with the added modification of removing the by-produced solid ammonium halide using ethylene diamine.
Verbeek et al, in U.S. Pat. No. 3,853,567 and U.S. Pat. No. 3,892,583 disclose that mixtures of CH.sub.3 SiCl.sub.3 and (CH.sub.3).sub.2 SiCl.sub.2 can be treated with ammonia or organoamines to form materials that can be pyrolyzed to yield SiC/Si.sub.3 N.sub.4 ceramic materials.
More recently, Gaul in U.S. Pat. No. 4,312,970, issued Jan. 26, 1982, disclosed the preparation of polysilazanes such as {(CH.sub.3).sub.3 Si}.sub.2 NH. In his synthesis, (CH.sub.3).sub.3 SiCl was eliminated as a by-product. These materials can be pyrolyzed at high temperatures to form Si-C-N containing ceramics. In addition, Gaul, in U.S. Pat. No. 4,404,153, issued July 20, 1982, disclosed preceramic polysilazanes which had been prepared by the reaction of chlorine-containing disilanes and disilazanes. Cannady, in U.S. Pat. No. 4,543,344 discloses polymers prepared by reacting HSiCl.sub.3 and disilazanes and later, Cannady, in U.S. Pat. No. 4,540,803, issued Sep. 10, 1985, described a modification to Gaul's earlier process to include the preparation of a polyhydridomethylsilazane polymer from HSiCl.sub.3, and hexamethyldisilazane.
Polymers have been developed and disclosed: by Gaul in U.S. Pat. No. 4,395,460, issued July 26, 1983; U.S. Pat. No. 4,404,153, issued Sept. 13, 1983; Haluska in U.S. Pat. No. 4,482,689, issued Nov. 13, 1984; Seyferth, et al. in U.S. Pat. No. 4,397,828, issued Aug. 9, 1983; and U.S. Pat. No. 4,482,669, issued Nov. 13, 1984; Cannady in U.S. Pat. No. 4,535,007, issued Aug. 13, 1985; Bujalski in United State patent application Ser. No. 653,003, filed Sept. 21, 1984, now abandoned; Baney, et al. in United State patent application Ser. No. 652,938, filed Sept. 21, 1984, now abandoned; and Ser. No. 653,939 filed Sept. 21, 1984, now abandoned Haluska United State patent application Ser. No. 925,145, filed Nov. 3, 1986 and application Ser. No. 926,607, filed Nov. 4, 1986, now U.S Pat. No. 4,742,143
In spite of an intensive search, however, the inventors herein were unable to find any suggestion or teaching in the art regarding the formation of polysilacyclobutasilazanes.